Denso SMT7 - Page 32

Chapter 2 Engineering Design of Servo Mechanism
16
4-1) Average load F
m
, Average rpm N
m
When shaft direction load is changed, find the average load which may give the life equal to the
fatigue life under changing load conditions, and calculate the life.
(a) When load and rpm are divided step-by-step (Fig. 2-5)
Shaft direction load
(kgf)
Speed (rpm) Time in use or rate of
time in use
F
1
F
2
٠
٠
٠
F
n
n
1
n
2
٠
٠
٠
n
n
t
1
t
2
٠
٠
٠
t
n
Average load F
m
can be achieved by the following equation.
Average load F
m

  
  






Fnt Fnt Fnt
nt nt nt
nnn
nn
1
3
11 2
3
22
3
11 2 2
13/
·············Equation (3)
And the average rpm can be achieved by the following equation.
N
ntnt nt
tt t
nn
n
m





 
11 2 2
12
·································································Equation (4)
(b) When load is changed almost linearly (Fig. 2-6)
Average load F
m
can be approximately achieved by the following equation.
FFF
m

1
3
2()
min max
················································································Equation (5)
Fig. 2-5. Step-by-step fluctuation load Fig. 2-6. Monotonous fluctuation load